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vacuum gauge recommendation?

Can anyone recommend a vacuum gauge for me? I'm going to need to do a throttle-body sync on a K100. Is the tool I need the same as a carb sync tool? Or is there a difference I'm missing? If you have any recommendations on where to get one that's reliable and inexpensive, I'd appreciate it.

a carb sync tool is the same thing. I'd get one for bikes that have 4 cylinders of course. Vary rarely would anyone need to sync throttle bodies or carbs on a modern bike, so wouldn't you know the tool is expensive. I think most of them are around $100. If you're feeling really handy there are plenty of websites out there that will show you how to make one using a meter stick, 6ft of clear tubing, a bunch of jelly jars, and some food coloring. You have to be really determined to save $100, because this thing will take a long time to make and get set up correctly. I gave up halfway through and decided that it wasn't worth my time to make one.

Now, are you sure your bikes TB's need to be adjusted? A lot of guys just want to tinker with stuff and they figure "I've never adjusted those so maybe they need it!" Let me tell you, "if it aint broke, dont fix it!" There's a reason why the adjusting the TB is not part of the regular maintenance on a K bike; it almost never needs to be done. if the bike is running ok, then you are more likely to mess things up than you are making them better. DAMHIK Whatever you decide to do, good luck!

Way to hit the nail on the head...something to fiddle with is always fun.

I don't know how to describe it, but the bike seems sort of wheezy. Something to do with the fuel/air mix. Sometimes on hard acceleration it pulls hard and then bogs around 5,500 RPM. Occasionally I can feel a surging in low revs.

At other times, however, neither symptom seems to exist. Last night, it pulled nicely all the way to a 7,000 RPM shift point, although it didn't seem to be building more power as its curve indicates.

The real TB sync - the relationship of the throttle plates - is set at the factory, then the screws to do it are sealed, for a reason. You'll never get it as good as it was done at the factory doing it on a live engine. The only "user" (dealer) adjustable part of the TB's is the idle sync - the BBS as it's known (Big-Brass-Screws) - and while you can improve idle with it - it will do absolutely positively for-sure nothing at all at 7,000 RPM.

MUCH more likely things to look at are:

1 - Fuel pressure - what's your fuel pressure at the fuel rail?
2 - Vacuum leaks - have you checked for them? Those nice TB's connect to the head with rubber mounts that are now 20 going on 30 years old. What'cha want to bet some of them could be leaking? How about the crankcase vent hose - been changed lately?
3 - CO been set? There is a mixture adjustment for that on the air-vane air-flow-meter.
4 - Injectors been cleaned lately (especially if the bike was left laying around for a while)? They can get gunked up if left sitting with stale fuel in them.
5 - When was the last time the valves were adjusted?

Someone once said about English cars - Carburetor is French for "LEAVE IT ALONE".. the reason SU Carbs got such a bad rep was people futzing with them. They really were a stone simple carb that gave almost no trouble if you just left them alone.

Same thing about the TBs. I think BMW should have taken it a step further at the factory and simply brazed all the adjustments in place once they were done flow-benching them... but they figured the green plastic cap, or green paint on them would be enough to keep people from "improving" things. Unfortunately - they were wrong, and some people have had to replace their TB assembly after trying to "balance" them.

Leave the TB balance to the opposed twins. The older ones of them have been known to need it.

BTW - if you really want one - you're welcome to mine. You just have to come get it (about 5 hour trip from Albany..) It's a mercury one - very accurate and impossible to dispose of... it's headed to the county toxic waste facility soon if no one wants it.

I like to tinker on things too so I understand the desire. One thing about the K bikes is that they really aren't set up to do a TB adjustment. On 4 cyl bikes that require adjustment there will be a nipple on each carb or TB specifically for the purpose of hooking up to a manometer. The K bikes dont have them, at least not that I've seen on my K75 and K1200. Plus there isn't an indication as to which TB is the "master" that you should take all the readings off of. I dont even think there are screws that you can mess with on the TB of the K bikes.

I got all excited about tinkering with mine last winter and then when I finally looked into how much time it would take and how easily I could screw things up, I decided the bike was running fine. This left me more time to do other things that winter

I like to tinker on things too so I understand the desire. One thing about the K bikes is that they really aren't set up to do a TB adjustment. On 4 cyl bikes that require adjustment there will be a nipple on each carb or TB specifically for the purpose of hooking up to a manometer. The K bikes dont have them, at least not that I've seen on my K75 and K1200. Plus there isn't an indication as to which TB is the "master" that you should take all the readings off of. I dont even think there are screws that you can mess with on the TB of the K bikes.

I got all excited about tinkering with mine last winter and then when I finally looked into how much time it would take and how easily I could screw things up, I decided the bike was running fine. This left me more time to do other things that winter

Actually - on the two valve K's - there are nipples on the TB's. and I expect that was continued on the 4V ones. But you're correct - it really is NOT meant to ever be touched. The best you could do adjusting it is hide some other flaw in the engine (like a misadjusted valve or vacuum leak..) The nipples come in handy for checking the idle sync (the BBS mentioned above.) My experience was (on a lot of K bikes) - if the engine was tuned properly, and the BBS were clean, and there were no intake leaks - the BBS's all ended up within 1/8 turn of each other for perfect idle balance. That's why the engines run so nice..